[HPsquared]

Hard to prove empirically either way, I think. Even if they do, it's then arguable if this is worth the noise pollution etc. Probably depends on the circumstances in any case, so any empirical result would be too specific to be of any use. Science!

[asdff]

A thief can disable your blaring car alarm in like 30 seconds. Enough time for anyone listening to go "wow someone must have hit the panic button in their pocket" and move on with their life.

[cmeacham98]

Car alarms are not useful for bystanders, they are useful for the owner of the car (who would know their alarm shouldn't be going off).

That said, this makes them near-useless in most public settings.

[asdff]

"That couldn't have been mine, someone already shut it off" They will think, as the thief disconnects their battery and loads the car on a flatbed.